1. Field of the Invention
The present invention relates to controlling the flow of a hot fluid and, in particular, to a closure member for an apparatus, such as a guillotine damper, for controlling such a fluid flow. A typical application for such an apparatus is control of the flow through a duct of hot flue gases from a power plant.
2. Description of the Prior Art
It is known to provide guillotine-type dampers for the control of hot fluids in a duct, typically hot flue gases from a power plant. Such a device is disclosed in U. S. Pat. No. 4,088,146 to the present inventor. In such an apparatus, the closure member or damper blade is movable between an open position, in which the damper blade is removed entirely from the fluid passageway of the damper, and a closed position, in which the damper blade extends entirely across the fluid passageway.
The closure member or damper blade is subject to differential heating when in the closed position. Hot gases impinge only upon the upstream side of the damper blade, causing a differential temperature between the upstream and downstream sides. In addition, the damper blade, even when in the closed position, has a portion which extends outside of the fluid passageway. The section outside the fluid passageway is not subject to direct impingement of the hot gases, thus causing that section to be cooler, resulting in further differential temperatures in different parts of the blade.
The result of the differential temperatures is stress and distortion of the damper blade, which in turn can lead to cracking and early failure, which may cause binding of the damper blade in the mechanism for moving it, and which may cause damage to other parts of the damper, such as the seals of the damper, when the damper blade is moved.
It has previously been proposed to divide damper blades, valve members or other heated components into sections to better accommodate differential heating. Such constructions are shown in U.S. Pat. Nos. 1,734,450 to Smith, 1,995,845 to Flintermann, 1,934,928 to Jackson, 1,932,243 to Clark, and U.S. Pat. Nos. 1,643,766, 1,798,460 and 1,991,016 to Fahrenwald.
Nevertheless, such sectional-type constructions have involved multiple pieces joined together throughout the structure, without regard to the particular hot or cold characteristics of each particular region of the component. The use of such multiple pieces creates sealing problems and complicates construction. The end result has been designs which are intricate, which would be expensive to build, and which may be subject to leakage problems.